There are two versions of each lab, one with a ten-question conclusion and one with directions for a full lab report. This way the teacher has the option! Each lab is two pages to allow for one two-sided handout.
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*Some of you have already purchased my lab book – be sure to check out Page 141 !
“Aerogel is a synthetic porous ultralight material derived from a gel, in which the liquid component for the gel has been replaced with a gas. The result is a solid with extremely low density and low thermal conductivity. Nicknames include frozen smoke, solid smoke, solid air, solid cloud, blue smoke owing to its translucent nature and the way light scatters in the material. It feels like fragile expanded polystyrene to the touch. Aerogels can be made from a variety of chemical compounds.
Aerogel was first created by Samuel Stephens Kistler in 1931, as a result of a bet with Charles Learned over who could replace the liquid in ‘jellies’ with gas without causing shrinkage.
Aerogels are produced by extracting the liquid component of a gel through supercritical drying. This allows the liquid to be slowly dried off without causing the solid matrix in the gel to collapse from capillary action, as would happen with conventional evaporation. The first aerogels were produced from silica gels. Kistler's later work involved aerogels based on alumina, chromia and tin dioxide. Carbon aerogels were first developed in the late 1980s.
Aerogel is not a single material with a set chemical formula; instead, the term is used to group all materials with a certain geometric structure.”
“Aerogels are a diverse class of porous, solid materials that exhibit an uncanny array of extreme materials properties. Most notably aerogels are known for their extreme low densities (which range from 0.0011 to ~0.5 g cm-3). In fact, the lowest density solid materials that have ever been produced are all aerogels, including a silica aerogel that as produced was only three times heavier than air, and could be made lighter than air by evacuating the air out of its pores. That said, aerogels usually have densities of 0.020 g cm-3 or higher (about 15 times heavier than air). But even at those densities, it would take 150 brick-sized pieces of aerogel to weigh as much as a single gallon of water! And if Michaelangelo’s David were made out of an aerogel with a density of 0.020 g cm-3, it would only weigh about 4 pounds (2 kg)! Typically aerogels are 95-99% air (or other gas) in volume, with the lowest-density aerogel ever produced being 99.98% air in volume.
Essentially an aerogel is the dry, low-density, porous, solid framework of a gel (the part of a gel that gives the gel its solid-like cohesiveness) isolated in-tact from the gel’s liquid component (the part that makes up most of the volume of the gel). Aerogels are open-porous (that is, the gas in the aerogel is not trapped inside solid pockets) and have pores in the range of <1 to 100 nanometers (billionths of a meter) in diameter and usually <20 nm.
Aerogels are dry materials (unlike ‘regular’ gels you might think of, which are usually wet like gelatin dessert). The word aerogel refers to the fact that aerogels are derived from gels–effectively the solid structure of a wet gel, only with a gas or vacuum in its pores instead of liquid. Learn more about gels, aerogels, and how aerogels are made."
“In their earliest days, aerogels were marketed as thickening agents and used in everything from makeup and paint to napalm. They were also used as cigarette filters and insulation for freezers. Monsanto was the first company to market aerogel's commercial applications. However, Kistler's supercritical drying method, though effective, was also dangerous, time-consuming and expensive. After 30 years of production, all these factors led Monsanto to discontinue its focus on aerogels in the 1970s.
However, this wasn't the end of aerogel. Not long after it was abandoned by Monsanto, scientists developed a process that made the production of aerogels less toxic by using a safer alkoxide compound. They also made it less dangerous by replacing supercritical alcohol with supercritical carbon dioxide in the drying process. These developments reduced the time spent drying the aerogels and reduced the hazardous and flammable nature of their production. Such advances made aerogel a bit more commercially viable again, and scientists grew intrigued by the product's possibilities.
As aerogel's production was made less complicated and dangerous, its unique properties have made aerogel popular with a range of industries. Silicon manufacturers, homebuilding materials manufacturers and space agencies have all put aerogel to use. Its popularity has only been hindered by cost, though there is an increasingly successful push to create aerogels that are cost-efficient. In the meantime, aerogels can be found in a range of products:
Because of aerogel's unique structure, its use as an insulator a no-brainer. The super-insulating air pockets with the aerogel's structure almost entirely counteract the three methods of heat transfer: convection, conduction and radiation [source: Cabot Corporation].
Even though aerogel is still quite expensive, the good news is that studies have shown that aerogel insulation used in wall framing and hard-to-insulate areas such as window flashing can save a homeowner up to $750 per year. In addition to helping homeowners save money, aerogel insulation can significantly reduce your carbon footprint. Companies are racing to find a way to bring costs down, but for now, aerogels are more affordable for NASA than the general public. Still, aerogels are put to use by construction companies, power plants and refineries. Perhaps when it's more affordable, aerogel will achieve that A-list status.”
“In general, gels are three-dimensional networks of solid, spanning the entire volume of a fluid medium. You're probably most familiar with hydrogels, where the fluid is water - think of Jell-O. Aerogels are composed of a solid network spanning a gaseous medium, instead of a liquid one. The substitution of gas for liquid means that the density of standard aerogel is the lowest of any known bulk solid.
The most common aerogels are made from silica, although metal oxides and organic materials have also been used. Silica aerogels have very, very low thermal and electrical conductivity, making them wonderful insulators. Metal oxide aerogels have similarly low density and high porosity, and are often used as chemical catalysts.
Aerogels are made by supercritically drying a liquid-phase gel, which ensures that the structure of the aerogel is maintained throughout the drying process. Supercritical drying avoids the liquid-gas phase transition by heating and pressurizing the material to above its critical point, whereupon it becomes a supercritical fluid.
The supercritical fluid has properties of both liquid and gas: very compressible, has no surface tension (due to lack of liquid-gas interface), diffuses through solids, and is still dense enough to support a solid structure. The supercritical fluid is then cooled and depressurized into the gas phase. If one were to evaporatively dry the liquid solvent - where the liquid is simply heated until it becomes a gas - the surface tension between the gas and the liquid would be too strong for the aerogel's delicate structure, and the gel would collapse. We built our own supercritical dryer for purposes of this project.”
Here is a 12 minute segment that has an interesting examination of the properties of Aerogels.
Notice that they do not wear goggles during the experiment. They make that choice probably because they’re melting food. The narrator also tastes the food being melted – also not a good choice for a lab situation.
This blog it about a topic that is more advanced than your typical Introductory Chemistry class. I include it for the teacher’s information and possible student reference.
Past blog posts about Final Exams and the End of the School Year include:
06/08/2014 Final Exams – End of Year Preparation
06/15/2014 End of Year Activity – Lab Clean-Up
06/29/2014 Summer Vacation
05/28/2015 Extra Credit II
06/11/2015 End of Year Reflection
06/04/2015 Final Exams II
06/19/2016 End of Year Reflection II
*This Blog contains several entries that would be helpful to your chemistry classroom. Check out the Topic List to help you to find past Blog entries.
Also, Write To Me about your successes, challenges, or questions in the Chemistry Classroom.
Remember, buying a copy of the lab book Chemistry on a Budget can be very useful to your Chemistry classroom with labs and class article ideas.
Have a great weekend!